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/* Copyright 2017 The ChromiumOS Authors
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*
* Tests entropy source.
*/
#include "common.h"
#include "console.h"
#include "rollback.h"
#include "test_util.h"
#include "timer.h"
#include "util.h"
#include "watchdog.h"
static int buckets[256];
static const int log2_mult = 2;
/*
* log2 (multiplied by 2). For non-power of 2, this rounds to the closest
* half-integer, otherwise the value is exact.
*/
uint32_t log2(int32_t val)
{
int val1 = 31 - __builtin_clz(val);
int val2 = 32 - __builtin_clz(val - 1);
return log2_mult * (val1 + val2) / 2;
}
void run_test(int argc, const char **argv)
{
const int loopcount = 512;
uint8_t buffer[32];
timestamp_t t0, t1;
int i, j;
uint32_t entropy;
const int totalcount = loopcount * sizeof(buffer);
const int log2totalcount = log2(totalcount);
memset(buckets, 0, sizeof(buckets));
for (i = 0; i < loopcount; i++) {
t0 = get_time();
if (!board_get_entropy(buffer, sizeof(buffer))) {
ccprintf("Cannot get entropy\n");
test_fail();
return;
}
t1 = get_time();
if (i == 0)
ccprintf("Got %zd bytes in %" PRId64 " us\n",
sizeof(buffer), t1.val - t0.val);
for (j = 0; j < sizeof(buffer); j++)
buckets[buffer[j]]++;
watchdog_reload();
}
ccprintf("Total count: %d\n", totalcount);
ccprintf("Buckets: ");
entropy = 0;
for (j = 0; j < 256; j++) {
/*
* Shannon entropy (base 2) is sum of -p[j] * log_2(p[j]).
* p[j] = buckets[j]/totalcount
* -p[j] * log_2(p[j])
* = -(buckets[j]/totalcount) * log_2(buckets[j]/totalcount)
* = buckets[j] * (log_2(totalcount) - log_2(buckets[j]))
* / totalcount
* Our log2() function is scaled by log2_mult, and we defer the
* division by totalcount until we get the total sum, so we need
* to divide by (log2_mult * totalcount) at the end.
*/
entropy += buckets[j] * (log2totalcount - log2(buckets[j]));
ccprintf("%d;", buckets[j]);
cflush();
}
ccprintf("\n");
ccprintf("Entropy: %u/1000 bits\n",
entropy * 1000 / (log2_mult * totalcount));
/* We want at least 2 bits of entropy (out of a maximum of 8) */
if ((entropy / (log2_mult * totalcount)) >= 2)
test_pass();
else
test_fail();
}
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